The goal of the pilot project is to establish the feasibility and potential value of using microelectrode techniques to measure local tissue PO2 in the eye especially the retina and choroid. The ultimate aim is to undertake a study of tissue PO2, pH and blood flow and their relationship to diabetic retinopathy and neovascularization. Hypoxia in the retinal tissue has been widely assumed to be associated with retinopathy; however, relatively few actual measurements have been made, presumably due to the technical difficulty. In this pilot project, detailed measurements of the PO2 profiles through the retina and choroid will be made using a compound beveled, research PO2 microelectrode developed and perfected in our laboratory. The tip locations will be marked by an iron deposition method. Serial sections of the retina will be made and a three dimensional map of structures of interest and electrode sampling sites will be generated. This, together with the histograms of the tissue PO2, should provide an exceptionally complete characterization of the tissue PO2 and clearly illustrate the potential of these techniques for comparison between the normal and diseased retinas. The experimental animals will be cats initially and finally dogs. All experiments will be acute and each animal will be sacrificed by barbiturate overdose followed by formalin perfusion.